Link adaptation is a fundamental technique in modern mobile communication systems. With link adaptation, the channel coding rate and modulation scheme is typically chosen based on so-called Channel Quality Index (CQI) reports. These CQI reports are derived at the receiver to reflect channel quality and interference levels, and subsequently transmitted over a signaling channel.
As an alternative, the CQI reports can be estimated directly at the transmitter, based on the quality of the transmissions received from the intended receiver.
The CQI reports are then used as a basis to select the channel coding rate and modulation scheme to transmit as much user data as possible using as little resources as possible. This is achieved by predicting the resulting block-error probability (BLEP) for each possible modulation and coding scheme (MCS). That is for each combination of modulation and channel coding the resulting BLEP is calculated and the currently best MCS is then selected based on the outcome of those calculations. If the channel quality reports provide an accurate measure of the channel quality at the transmission instant, it becomes possible to maintain tight control over the BLEP when transmitting a data stream.
For several reasons however, the channel quality during transmission is different from the channel quality indicated by the CQI reports. At least three factors will cause the actual channel quality to deviate from the channel quality in the CQI reports:                The CQI reports are old, i.e. the channel and/or interference levels may have changed since the measurement.        Estimation errors.        The CQI reports are quantized.        
These inaccuracies are well-known and attempts have been made to reduce them. Although successful to some extent, the improved estimation methods leave significant inaccuracies in the CQI estimates resulting in that the non-optimal modulation and coding scheme is selected for transmission.
Hence, there exist a need for an improved method and system for determining the modulation and coding scheme based on a channel quality value such as a CQI report.